<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>十字路口</title>
    <link href="https://cdn.bootcss.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
    <style>
        #main {
            margin: 100px auto; 
            width: 1000px;
            height: 400px;
            background: #0b182b;
        }
        select {
            margin-left: -46px;
            padding: 5px 20px;
            position: absolute;
            top: 50px;
            left: 50%;
        }
    </style>
</head>
<body>
<div id="main"></div>
<select id="direction">
    <option value="3">直行</option>
    <option value="2">左转</option>
    <option value="1">右转</option>
    <option value="4">直行左转</option>
    <option value="5">直行右转</option>
</select>
<script src="https://cdn.bootcss.com/require.js/2.3.5/require.min.js" data-main="main"></script>
</body>
</html>